SQL - top 20 records

SELECT
-- Columns
      FIELD
-- Tables
      FROM LIB/FILEX AS A
-- Where
      WHERE 19 >=
            ( SELECT COUNT(*)
              FROM LIB/FILEX AS B
              WHERE B.FIELD_COUNT > A.FIELD_COUNT
                AND A.KEY1 = B.KEY1
                AND A.KEY2 = B.KEY2